The invention disclosed herein relates to hoisting apparatus in general, and in particular to hoisting apparatus which employs buoyant forces generated within a liquid body to move loads outside of the liquid body.
U.S. Pat. No. 5,016,551 (Peck et al.) discloses a lift for water vehicles which utilizes a tank situated in the water below a vehicle to lift the vehicle out of the water by displacing water within the tank with air. U.S. Pat. No. 2,313,215 (Bierlee) discloses apparatus for raising submerged vessels which utilizes collapsed bags that are inflated to produce the buoyancy to raise the vessel. Both of those patents are directed to lifting vessels in water.
U.S. Pat. No. 2,470,312 (Levin) discloses a reciprocal buoyancy lift which utilizes buoyancy to move compartments in two spaced housings which are almost entirely submerged in a body of fluid. A compartment in a first of the two housings has a fixed buoyancy and the buoyancy of a compartment in a second housing may be selectively changed by introducing therein or venting therefrom compressed air. The compartments in the two housings are selectively communicated to selectively transfer fluid therebetween. After compressed air is introduced into or vented from the compartment in the second housing, and that compartment moves up or down, respectively, fluid is selectively transferred between the compartments so that they mutually assist each other in moving in opposite directions. The lift disclosed in the Levin '312 Patent is relatively complicated, and as disclosed does not appear to be suited for moving loads entirely outside of the fluid body.
There is a need for simplified apparatus which uses buoyant forces to move loads outside of the liquid body in which the buoyant forces are generated.